The present invention relates to the construction of micro-electro mechanical devices such as inkjet printers and in particular discloses a process of electrical isolation of components from a fluid reservoir.
Recently, for example, in PCT Application No. PCT/AU98/00550 the present applicant has proposed an inkjet printing device which utilizes micro-electromechanical (MEMS) processing techniques in the construction of a thermal bend actuator type device for the ejection of fluid from a nozzle chamber.
In any such thermal actuator type device, it is often the case that the thermal bend actuator is operated via the selective resistive heating of an element. The utilization of conductive heating elements near a fluid supply may lead to problems whereby the fluid supply interferes with the electron flow in the conductive element and electrolysis results. This can result in a general breakdown of the actuator leading to catastrophic failure.
It is an object of the present invention to provide for the electrical isolation of a conductive resistive heating element from a fluid supply.
In accordance with a first aspect of the present invention, there is provided an inkjet printhead constructed by micro-electromechanical (MEMS) processing techniques with a plurality of ink ejection nozzles, each nozzle comprising
a substrate;
a chamber-defining portion arranged on the substrate to define a nozzle chamber and a nozzle opening in communication with the nozzle chamber;
a pit located at least partially around a rim of said nozzle opening, said pit being adjacent said chamber-defining portion and extending from a level of said nozzle opening towards said substrate;
a thermal bend actuator arranged on the substrate externally of the nozzle chamber defining portion, the actuator having a proximal end anchored to the substrate and a distal end connected to an ink ejection paddle arranged within said chamber; and
the thermal bend actuator comprising a series of layers, one of said layers being a planar conductive heating circuit layer having a first portion extending from said proximal end towards said distal end and forming a planar conductive heating circuit for beating said thermal bend actuator, and a second portion extending from said ink ejection paddle towards said proximal end, said second portion being electrically isolated from said first portion by means of a discontinuity in said planar conductive heating circuit layer, said discontinuity being located externally of said nozzle chamber.
The planar conductive heating circuit layer can comprise substantially titanium nitride. A first portion of the planar conductive heating circuit layer preferably can include a tapered slot portion widening towards the proximal end so as to increase resistive heating adjacent the proximal end.